In a yarn feeder of this kind as known from WO95/20700, the carrier ring can be moved reciprocally by means of shift drives forwards and backwards exclusively over one and the same travel stroke within the axial clearance in the holder. Since the holder can be adjusted in the bracket in the axial direction, the braking effect between the braking body and the yarn withdrawal region of the storage drum can also be adjusted, either when the carrier ring abuts at an axial counter stop or the carrier ring abuts the opposite axial counter stop. However, the travel stroke of the carrier ring cannot be varied by this adjustment, i.e. the difference between the braking effect in both abutting positions. It is disclosed to adjust the travel stroke of the carrier ring between its axial counter stops of the holder by inserting or removing disc washers from an axial counter stop intended for one moving direction of the carrier ring in the housing. However, this is time-consuming and necessitates a partial disassembly in the region of the holder.
It is an object of the invention to improve a yarn feeder of this kind such that the travel stroke of the carrier ring within the predetermined axial clearance in the holder can be varied comfortably and rapidly in order to vary the difference between the braking effects in both end positions of the carrier ring in addition to the already possible adjustment of the holder.
The above object can be achieved by providing a yarn feeder with a carrier ring which is axially shiftable in a ring-shaped holder within a predetermined clearance defined by counter stops of the holder. Further, at least one pair of shift drives are provided on the holder for axially shifting the carrier ring between the counter stops, and the carrier ring defines thereon at least one travel stroke adjustment ramp for adjusting the stroke of the carrier ring within the predetermined clearance. The carrier ring is rotatable relative to holder so as to align the ramp with a first of the counter stops which faces the ramp facing counter stop.
By rotating the carrier ring in said holder, the travel stroke of the carrier ring can be varied simply and rapidly between its end positions, since the first axial counter stop of the holder is then in a co-operating position.
In one embodiment, an additional axial counter stop is provided, which also co-operates with a travel stroke adjustment ramp in order to create another adjustment possibility for the travel stroke of the carrier ring in the holder.
According to another embodiment, the axial side surface of the carrier ring or the plane of the axial side surface of the carrier ring may itself form a travel stroke adjustment ramp within the ramp group.
Several travel stroke adjustment ramp groups may be distributed over the circumference of the carrier ring in order to guarantee a stable support of the carrier ring.
A particularly advantageous embodiment includes housings located at a removal opening of the holder, which housings form the first axial counter stop which may be selectively brought into co-operation with the travel stroke adjustment ramps of each group.
In another embodiment, at both axial side surfaces of the carrier ring, groups of travel stroke adjustment ramps are provided, and groups of counter stops are provided at both axial sides of the holder. In this way, a plurality of adjustment possibilities for the travel stroke of the carrier ring are achieved.
In yet another embodiment, three travel stroke adjustment ramps are provided which satisfy in practice all requirements regarding the variation of the travel stroke of the carrier ring.
In still another embodiment, the carrier ring can be comfortably rotated in order to vary the travel stroke via inclined transition surfaces provided between the respective ramps. The inclined transition surfaces in addition produce clearly grippable movement transitions.
Rotational limiting abutments prevent an excessive rotational adjustment of the carrier ring.
In a further embodiment, the co-operation between each axial counter stop and one travel stroke adjustment ramp takes place at a location circumferentially offset relative to the shifting drive.
In a still further embodiment, the first axial counter stop is located in the region of the shift drive. In the case where the travel stroke adjustment ramps are provided at the axial side of the carrier ring facing the first axial counter stop a receiving cut-out follows or is located adjacent the first axial counter stop. The receiving cut-out occasionally acts as a further axial counter stop, allowing the co-operation between the first axial counter stop and a lower travel stroke adjustment ramp, since a higher travel stroke adjustment ramp is able to enter the receiving cut-out.
In an alternative embodiment, the shift element of the shift drive itself forms the first axial counter stop of the holder, which first axial counter stop co-operates with the carrier ring or the travel stroke adjustment ramps, respectively.
In another embodiment, the shift elements loading the carrier ring in a direction towards a weak braking engagement or release position are actuated pneumatically or magnetically only upon demand, while the shift element acting in the opposite direction is effective permanently.
In yet another embodiment, both shift drives of a pair are pneumatical or magnetic shift drives which preferably are actuated actively and selectively in both shift directions.
The carrier ring according to the invention may be formed of plastic and the travel stroke adjustment ramps integral therewith. This embodiment is simple in terms of manufacturing. The groups of travel stroke adjustment ramps can be formed with only a few structural molding steps.
In one embodiment, markings are provided so as to visually display the selected travel stroke.
Also a projection may be provided to assist in rotation of the carrier ring.
In another embodiment, the carrier ring equipped with the travel stroke adjustment ramps is provided on a braking body fulfilling the braking effect by means of resilient bristles, fingers, lamellae or by means of a resilient annular membrane having a brake lining. The basic braking effect can be set by means of the axial displacement device of the holder in the bracket. The travel stroke of the carrier ring in the holder due to the travel stroke adjustment ramps is variable, such that the difference between the braking effects in both end positions of the carrier ring can be varied.